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DoctorDiff "Out-of-stock" 8 3/4" 489 Case Third Member Want to Source a 3:23 Sure Grip ASAP

road robert

road robert

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DoctorDiff "Out-of-stock" 8 3/4" 489 Case Third Member – Seeking New 3:23 Sure Grip ASAP!

Oh no! Should have thought about this last Winter - I finally decide to pull the trigger ready to swap my tired (and scary loud) 3:91 with leaky axle and contacted the good Dr. (Cass via text) today and he has no lead time on one and suggested I reach out to Tom Hild ([email protected]) to build a third-member around his Sure-Trac helical differential (I did email him).

Does anyone know an alternate source for a new 8 3/4 489 Case third member with 3:23 sure grip plug & play unit? I want to swap the entire third member with a complete plug and play 3:23 sure grip unit with a (matching spline) axle package with bearings installed. I do not have the time or tools or know how to rebuild my unit and press on and off tapered axle seals.

DoctorDiff does have: Axle package stock length Mopar 5 x 4 1/2 bolt pattern pair with the bearings installed $298.00

Also need to confirm that the U-joint clamps match up to whatever I currently have to make this as simple as possible. I know about the bearing debate but Dr. Diff said the green bearings are OK. My motivation and deadline is to participate in our own “Power Tour” happening soon - end of May…

Please help, Thanks!

road robert

P.S. I live in Massachusetts so if anyone knows a good shop to convert mine and/or do axle bearings that could be an option.
 
This is our local specialist.
He's done thousands.
You could give him a call he's a good guy.
Screenshot_20250325-210711.png
 
There are no seals for the axle bearings just a gasket for the 5-bolt flange. There are on the other hand "inner" axle seals that are very easy to change, they go inside the housing ends. No need to press axle bearings on or off. It is really an easy operation to change out the 3rd member, except for the weight and mess of it. To set axle end play is not hard either. Make sure the 3rd member you buy has the thrust button in the middle of it or else axle end play will be impossible to set and you will eat bearings. I would stick with the factory tapered bearings as well. Greens are ok, but the tapered are far superior.
 
velocityss1985 said:
There are no seals for the axle bearings just a gasket for the 5-bolt flange. There are on the other hand "inner" axle seals that are very easy to change, they go inside the housing ends. No need to press axle bearings on or off. It is really an easy operation to change out the 3rd member, except for the weight and mess of it. To set axle end play is not hard either. Make sure the 3rd member you buy has the thrust button in the middle of it or else axle end play will be impossible to set and you will eat bearings. I would stick with the factory tapered bearings as well. Greens are ok, but the tapered are far superior.
Click to expand...
Velocity1985: Wouldn't every "plug & play" third member come with a thrust button in the middle? And if I buy an axle package with green bearings installed doesn't that eliminate the need to set the axle end play? Trying to keep this simple and I do not know what condition my existing axle bearings are in and if they're worn out. Also seeing a few "posi" options such as:
Powerlock Posi
Sure-Trac (Dr. Diff exclusive?)
Is the 489 case the best and all for 30 spline axles, and is pinion spline compatible? I see different yoke sizes too.
The more I investigate and learn the more confused I get! lol
 
road robert said:
Velocity1985: Wouldn't every "plug & play" third member come with a thrust button in the middle? And if I buy an axle package with green bearings installed doesn't that eliminate the need to set the axle end play? Trying to keep this simple and I do not know what condition my existing axle bearings are in and if they're worn out. Also seeing a few "posi" options such as:
Powerlock Posi
Sure-Trac (Dr. Diff exclusive?)
Is the 489 case the best and all for 30 spline axles, and is pinion spline compatible? I see different yoke sizes too.
The more I investigate and learn the more confused I get! lol
Click to expand...
Yes, they should come with a thrust button, but if you get it from some random supplier or used it may not. Not a big deal to install one either. The 3rd member doesn't have to come apart. Yes, with the green bearings I would remove the thrust button, because there is a chance of extra side load to the green bearing if the axle touches the thrust button, which in theory will shorten the life span of the bearing. The only way to check the condition of the tapered is to pull the axle, since you mention you have a leaky side I would focus on that bearing to see if the grease was washed out by the gear oil and chewed up. There is a chance of that. Powerloc are clutch style suregrips and Sure-trac I believe is helical design. I have had good success with the powerloc units. Stay away from the Auburn or cone style units. 489 is a good case with the crush sleeve eliminator kit. 742 is a good case as well since there is no crush sleeve. 741 would be my last choice. There are 2 mopar yokes, 7260 and 7290. That's an easy measurement to determine which one you have. Measure the inside dimension of the yoke, (between where the caps of the u-joint mounts) on the 8 3/4. The 7260 (2-1/8" yoke ID) and the 7290 (2-5/8" yoke ID). The cap diameter for the 7260 is 1.078". The cap diameter for the 7290 is 1.126". This is all really simple stuff. Take a couple pics and I can guide you through it. You have a jack and stands correct? Also there are two different pinion splines 10 and 29 spline. I would also get the yoke with the u-bolts not the straps if you are going to beat on the car. The right side of the car is the adjuster side too.
 
Just got some 8 3/4 stuff from Quickperformance.com and they had everything I needed. Going to 1350 U-joints and they had quoted me $1100 for complete New nodular 742 housing with Power Lock type in it and 3.23 gear. I prefer Trutrac but $$$. More than competitive pricing.
 
Below is the breakdown from the DoctorDiff referral Tom Hild of Lake Havasu City, AZ :

"Here is a quote for the complete third member we discussed.

Mopar 8.75 3.55 Sure Trac in a 489 case with 7290 yoke, including the following;
- New heavy duty nodular iron 489 case with forged caps and billet adjusters.
- New helical gear Sure-Trac sure grip unit.
- New 3.55 ratio 29 spline ring and pinion gear set.
- New Timken USA bearings.
- New grade 8 ring gear bolts.
- New pinion seal.
- New solid pinion bearing spacer. [ eliminates un-reliable crush sleeve]
- OEM 7290 pinion yoke.
- Set up to factory specs with precision.

The total cost for the above would be $2100. including shipping and insurance to zip code 01520."

Not cheap but he called me and we talked for 1hr 45 mins the other night and I trust him, he is 71 years old. He prefers Zelle as the payment method. As they say you get what you pay for and buying online is always a risk but I trust and feel comfortable about this.
 
X2 for Quick Performance, competitive price and in stock. Built with selected parts and shipped when promised.
 
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